all: remove 1.8 and 1.9 from Travis builds
all: remove 1.8 and 1.9 from Travis builds

1.8 no longer compiles, and 1.9 is no longer supported.

Change-Id: I85cd9fb22dfac97486cf4e4e02cdc936af41cc31
Reviewed-on: https://go-review.googlesource.com/c/144179
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>

golang/lint